I have collected all sorts of things in the past (action figures, Comics, cards, original art) , but thankfully I have grown out of that phase of my life.
I still collect trilobites, but I keep it reasonable, I am only looking for a few select species, and only those that are excavated with the utmost care. I have 8 trilobites in total, most of them are in poor shape, and not really display worthy. The centerpeice of my collection was a 4.5 inch, 450 Million Year Old Russian Asaphus Punctatus fossilized in sandstone, a museum quality piece. When I moved in with my girl friend, she dropped it while cleaning and it shattered into about 30 pieces. The first thing she asked "was it rare? or valuable?" She almost fainted when I told her it was worth any where from $500 to $800 and was 450 Million Years old.
Oh well, now at least I have another species on my hit list of must have's.
http://www.stonesbones.com/020807k.jpg
Here is an example of the fossil I had, mine was about an inch and a half bigger.